It has hitherto been known that a higher piezoelectric coefficient is exhibited in a piezoelectric thin film composed of an aluminum nitride containing scandium as compared with a piezoelectric thin film composed of an aluminum nitride containing no scandium. However, scandium is very expensive since scandium is not industrially widely used, and has also been difficult to be stably obtained. As such, research on aluminum nitride containing an element other than scandium have been widely conducted.
For example, the following Patent Document 1 discloses a piezoelectric thin film composed of an aluminum nitride film containing a divalent element and a tetravalent element and an aluminum nitride film containing a divalent element and a pentavalent element. In Patent Document 1, in an aluminum nitride film containing Mg as a divalent element and Zr as a tetravalent element, the enhancement in piezoelectric coefficient of the obtained piezoelectric thin film has been confirmed.
Patent Document 1: JP 2013-219743 A